Art of producing ground wood pulp



. UNITED STATES PATENT OFFICE.

EDWARD F. MILLARD, OF JACKSON, MICHIGAN.

'ART OF PRODUCING GROUND wooo PULP.

SPECIFICATION forming part of Letters Patent No. 449,586, dated March 31, 1891.

Application filed September 8,1890. Serial No. 364,330. (No specimens.)

To all whom it may concern.-

Be it known that I, EDWARD F. lVIILLARD, of Jackson, in the county of Jackson and State of Michigan, have invented a new and useful Improvement in the Art of Producing Ground lVood Pulp, of which the following is a specification.

My invention relates to the mode of manufacturing pulp such as is used as paper-stock and for other purposes.

The cheapness of ground wood pulp as compared with other forms of paper-stock, such as rags and chemically-prepared pulp of wood or straw, has led to its extensive use; but its inferior quality has limited its use.

As heretofore practiced, woods of suitable quality have been exposed to the action of grindstones under a pressure which may be approximately stated as ranging at from ten to twenty pounds to the square inch of the surface of wood exposed to the action of the stones.

In operating the machines it has been found that when the stones are sharp they produce an excessive proportion of short granular particles resembling and technically called sawdust. As the stones become dulled from use, or, as it is said, smooth, the quality of the product is improved by the diminution of the sawdust, the stones rolling up longer pieces; but still a considerable proportion of quite fine particles is produced, resulting in making what is called, technically, slow pulp that is to say, pulp which, when used in the paper-machines, causes the water to escape slowly from the pulp, thereby reducing the amount of paper produced in a given time, and also afiecting the evenness of the distribution of pulp on the wires and producing uneven paper. The smooth stones produce an increased prop0rtion of fiber; but the filaments which are rolled off will be found, on examination, to be of substantially uniform diameter, blunt -atthe ends, so that When made into paper main in the pulp and deteriorate its quality.

As the stones become still smoother, their efficiency is gradually impaired until it becomes necessary, at longer or shorter intervals, according to the quality of the stones, to resharpen them by the use of a bush-roll or bush-hammer. As a consequence of this irregularity of action, the product is not uniform, and its quality is such that it requires to be mixed with other and more expensive stock in order to produce merchantable paper.

The object of my invention is to produce wood pulp which is substantially uniform in composition, andis made up, as nearly as possible, of fibrous filaments which taper from the middle toward each end, and which therefore can be formed into paper of better quality than any which has been heretofore obtained from ground wood pulp. This end I accomplish by using under light pressure always sharp stones, the points of which catch the fibers of the wood and draw them from the sticks in pieces of considerable length as compared with their thickness without cutting or breaking them into sawdust or slivers, as is the case where the machines in common use are used with sharp stones under heavy pressure. The change in the result accomplished is due to the change in pressure. It is difficult in this, as in other cases, to state with precision the exact amount of pressure, as that must depend, to a considerable extent, upon the character of the wood under treatment, and also upon that of the stone; but it may be approximately given at from two to three pounds to the square inch of the wood surface exposed to the action of the stone. The change of pressureresults in a change in the character of the product, which, instead of being made up of The diltcrence in the result is such as to ofier an infallible guide to the operative in estab lishing the pressure at that which will produce the improved pulp which no skilled person would mistake for the pulp now generally made after having become familiar with the pulp produced by my process.

The pulp produced by my improved process is treated in the same manner as other ground pulp, either by forming it into shape for shipment as pulp or by passing it directly to the paper-engines as it is ground, when the mill is organized both as a pulp and paper mill. 

